Digital Fabrication Laboratory

The College of Design has two CAMaster CNC Routers with Automatic Tool Changer(ATC). Workshop technicians oversee all operation of the CNC router. After Workshop staff review and start your file, users are required to observe the router while it is in operation. Only Workshop personnel may start the CNC router.

Access to the CNC router is open to all CDES students for course related work - UofM departments outside of CDES should contact digifab@umn.edu to inquire about utilizing the CNC router: the rate for external work is $100/hr.

Cost:

To encourage efficient and sustainable use of limited resources and to cover tooling, maintenance and replacement costs we will be charging $5 per 15 minutes for CDes coursework: To encourage learning and self-sufficiency, we will be charging an additional $5 per 15 minutes of file set-up time: the first 15 minutes is free, so if you take the time to ask questions and to learn the required software (RhinoCam) costs are pretty minimal.

Overview

The CNC router can be used for cutting 2D part files and for 3D machining. The CNC router has a 4’x8’ bed and 10” gantry clearance (Z height). A 4” maximum Z height is a good rule of thumb, but the maximum Z height depends on many factors including tool length, tool clearance and part geometry. For 2d cutting, there should be a 1” margin around the perimeter of your material stock to screw into the router spoil board. The router is a 3-axis router, therefore it cannot make undercut or bevel cuts. A rotary indexing lathe with a maximum capacity of 12" dia x 48" is also available.

MATERIALS THAT CAN BE CUT INCLUDE:
Solid hardwood or softwood
Plywood, MDF, particle board and other sheet stock
Rigid insulation foam
Plastics, such as acrylic and polyethylene (LDPE / HDPE)

Preparing Your Files For CNC

There are five steps involved in preparing files for the CNC router.

STEP 1: DESIGN
Design can be done in many applications (Rhinoceros, AutoCad, Illustrator, SolidWorks, SketchUp, etc). 2d cutting requires only 2d line drawings. 2d cut parts should have each part represented as a single closed curve, path or polyline. Be sure your lines meet exactly at endpoints and there are no duplicate, intersecting or overlapping lines. 3d machining requires a polygonal mesh, a surface or solid model. All files should be scaled to the actual size and units of the output that you require.

STEP 2: TOOL PATHTool-paths need to be generated to program the machine to cut your part. We use RhinoCAM which is a plug-in that works within Rhinoceros. RhinoCAM is installed on all PC's in Rapson Hall computer labs and the workshop. We have a college-wide license for RhinoCAM that permits installation on students' computers: ask a shop technician for installation instructions and the server address. Rhino will import geometry from most 2D and 3D software programs. The three most commonly used operations in RhinoCAM are profiling (cutting), horizontal roughing (rough cutting of surfaces) and parallel finishing (finish cutting of 3d surfaces).

SELECTING CUTTING TOOLSGenerally, you should select the biggest diameter and shortest cutting tool you can safely use.
When selecting the tooling you’re going to use, keep in mind that you want to use an appropriately sized cutter for your job. The cutter’s diameter and length should be scaled for the amount and type of milling you plan on doing.

BASIC GUIDELINES FOR TOOL SELECTION:

The larger diameter the cutter, the more material it can remove per pass resulting in faster processing.
Smaller diameter cutters can get into tighter corners, but aren’t suitable for hogging out a lot of waste material.
Long cutters are used where there are drastic slopes and deep pockets that might cause the collet to crash into the work piece.
Short cutters are robust; they allow for more material removal per pass.
Square end mills are ideal for roughing passes.
Ball nosed end mills are not for roughing passes. They are used for finishing passes.

For example, if you need to rough mill a stepped topography that is 24” square and 2” tall, you should choose an end mill that will remove a lot of material. A medium length .75” or .5” end mill will allow you to rough out the topography quickly. You may then run a finishing tool pass with a medium length .25” end mill to clean up any small corners where the larger end mill couldn't reach.

STEP 3: REVIEWBefore your part is cut, a Workshop Technician will review the file. We will look for errors and suggest appropriate tooling and toolpath modification. If your RhinoCAM file is approved, the Technician will “post” your file. “Posting” creates a machine-readable text file (G-code) which is specific to our machine and our tool change operation. Only Technicians have the correct post-processor for our machine set-up: do not post files on your own. Once your file has been posted, we will schedule a time for you to run your part on the CNC router. Do not expect that this part can be run immediately. It is advisable to have your RhinoCAM file reviewed several days in advance of your desired cutting time.

Material PreparationStudents must supply their own materials. If your material stock is glued up, be sure that it has had sufficient time to dry. Use liberal amounts of glue spread evenly across the material to ensure complete adhesion when laminating materials. Also please note your actual material thickness, as this may effect your RhinoCAM settings. Calipers are located in the Workshop to get the exact thickness of your material. For example, if using 3/4” plywood, it is likely the actual thickness is .6875”. These exact dimensions must be used in RhinoCam.

STEP 5: Machine Set-Up and Operation

The processing of CNC jobs is at the sole
discretion
of Workshop staff: we will prioritize
jobs based on estimated cut time, staff workload
and user preparation and availability.
Having an appointment is not a guarantee of
machine availablity or completion of work.

Technicians will advise you on how best to secure your stock to the router table. Be aware of where you are placing screws to ensure that they are not in the way of a tool path. If a tool path hits a screw, the bit can be destroyed. If bits are broken due to carelessness, students are responsible for the cost of the bit (which can be more than $100 depending on the bit).
Workshop Technicians will help you set the machine for your part and instruct you on how to make a tool change if necessary. Users are responsible for observing the machine while in operation. Please note that it is common for parts to take several hours to finish. The estimated time from RhinoCAM should be tripled for actual run time, including material attachment, etc.

Users are required to wear safety glasses while the machine is in operation: hearing protection is also recommended.

Clean-Up

Users are responsible for leaving the area in a clean condition. There is a dust collection system that will pick-up the majority of dust. When your part is completed, you should blow the majority of the chips off of the machine and sweep the floor, putting off-cuts and scraps into the scrap racks or the dumpster. Cut large scraps down to rectangles for reuse. Do not leave large scraps in the router room. You may lose your privileges to use the CNC router if you are negligent in your clean-up responsibilities.

Questions

If you have questions about the CNC router, please drop by the Workshop and speak to a Technician.